Assignment Practical #3
Scanning Tunneling Microscope
1. Describe the working principle of a Scanning Tunneling Microscope (STM) and its major components (no more than 200 words). Which variable does the STM attempt to keep constant as it scans?
The STM uses 2 main principles, the piezoelectric effect which allows the tip to scan with angstrom-level control and the tunnelling effect is where the electrons move across a barrier it shouldn’t classically cross, but in the nanoscale quantum properties apply and electrons are also wave like, and will allow the computer to produce the surface of the nanomaterial. The Constant variable in the STM is the current.
2. The tip of a STM probes the….of a sample surface. Does the scan depend on the STM bias voltage? Why?
The scan does depend on the STM using bias voltage as it is thisthat allows the current and the distance between the tip and the sample to be kept constant.
3. Why can the STM scan sample surfaces with atomic resolution? On which major factors the density of states depend? Describe other major applications for STM?
Since the tip is a single atom, this allows the current between the tip and the sample to be in accordance to each atom giving a resolved image atomic detail. The density of states depends majorly on the energy, atomic structure and composition as the density of states is very similar and very closely related to the sample topography.
4. Can a STM displace iron atoms on a copper surface at standard conditions?
At standard conditions the iron atoms and the copper atoms in the surface being scanned cannot be effectively or precisely displaced due to the energy of the atoms being high and causing them to vibrate and these vibrations make it difficult to displace atoms accurately or precisely.